Magnetically commutated brushless d.c. torque motor

ABSTRACT

A brushless direct current motor operating through the interaction of a permanent magnet field with a commutated electro-magnetic field of changing polarity wherein current is carried from the external circuit to the windings of the armature by magnetic reed switches, each switch connected at one end to the external circuit and at the other end to the terminal of successive armature windings. The switches are placed in two circular arrays, each array containing in this instance 33 equiangularly-aligned members. A rotating magnet and plate assembly with two permanent magnet locations facing each of the arrays sequentially closes switches in two pairs, each pair consisting of one switch in the first array and one in the second array, to energize the armature windings at each operative position of the rotating magnet and plate assembly.

United "States Patent Ruschmann [151 3,662,196 51 May 9,1972

[54] MAGNETICALLY COMMUTATED BRUSHLESS D.C. TORQUE MOTOR [72] Inventor:Fred Ruschmann, Port Washington, NY.

[73] Assignee: Kollsman Instrument Corporation, Syosset, NY.

[22] Filed: Aug. 12,1970

[21] Appl.No.: 63,169

FOREIGN PATENTS OR APPLICATIONS 1,223,022 8/1966 Germany ..335/206Primary Examiner-.1. D. Miller Assistant Examiner-R. Skudy Attorney-E.Manning Giles and J. Patrick Cagney [5 7] ABSTRACT A brushless directcurrent motor operating through the interaction of a permanent magnetfield with a commutated electro-magnetic field of changing polaritywherein current is carried from the external circuit to the windings ofthe armature by magnetic reed switches, each switch connected at one endto the external circuit and at the other end to the terminal ofsuccessive armature windings. The switches are placed in two circulararrays, each array containing in this instance 33 equiangularly-alignedmembers. A rotating magnet and plate 56] References Cited assembly withtwo permanent magnet locations facing each of v the arrays sequentiallycloses switches in two pairs, each pair UNITED STATES PATENTS consistingof one switch in the first array and one in the second array, toenergize the armature windings at each operative 3,297,891 l/1967 Foran..310/46 position ofthe rotating magnet and plate assembly. 3,546,50712/1970 Wengel..... ....3l/46 3,497,997 3/ 1970 Sheckells ..335/206 6Claims, 4 Drawing Figures 5 a, i 35 s 34A 3{ m 24 a, w v

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ATTORNEY MAGNETICALLY COMMUTATED BRUSHLESS D.C.

TORQUE MOTOR 1 BACKGROUND AND SUMMARY OF THE INVENTION The motorconstructed according to the present invention is a permanent magnetdirect current motor. These motors operate through the interaction of afixed permanent magnet field with a second relatively movable magnetfield having a changing polarity, i.e., the armature. It is conventionalto change the polarity of the rotor field or commutate by means offriction contact brushes. In accordance with the present invention, thefriction contact brushes and their inherent problems are eliminated andthe necessary commutation is performed through the action of a novelswitch arrangement. Current is carried from an external circuit to thearmature windings through switches arranged in two circular arrays andequiangularly spaced within each array. Each switch is con nected at oneend to the external circuit and at the other end to one end of anarmature winding group. The switches are actuated in selected pairs,consisting of a switch from each array, by a rotating activatingassembly; thereby, energizing the required annature windings.

As the activating assembly rotates, it sequentially closes switch pairsto activate the selected armature windings. Rotation of the motor shaftis continuous because the activating assembly operates in such a mannerthat each initially-closed switch does not open before the next switchin the line of rotation is closed.

This arrangement is particularly useful for extending the life of a dc.motor in hard vacuums, in explosive and corrosive atmospheres, and inundersea and other environments where the maintenance required for acontact brush motor is particularly difficult. This constructionmaintains a dc. torque motors inherent advantages of slow speed, hightorque, fast response, speed control, positioning accuracy, etc.

No additional electronic circuits or controls are required for operatingthis brushless d.c. torque motor than are required for operating aconventional friction brush type do. torque motor.

Other features and advantages of the invention will be apparent from thefollowing description, and claims, and are illustrated in theaccompanying drawings which show structure embodying preferred featuresof the present invention and the principles thereof, and what is nowconsidered to be the best mode in which to apply these principles.

BRIEF DESCRIPTION OF THE DRAWINGS In the accompanying drawings forming apart of the specification, and in which like numerals are employed todesignate like parts throughout the same:

FIG. I is a cross-sectional view through the vertical axis of apreferred embodiment of the invention;

FIG. 2 is a front view of one of the circuit boards containing the reedswitch array;

FIG. 3 is a front view of the magnet and plate assembly; and

FIG. 4 is an illustration of an alternative embodiment of the inventionin which the armature windings are connected directly to the reedswitches.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT As shown in FIG. 1, themotor constructed according to this invention consists of a stationaryassembly and a rotating assembly 40. I

The stationary assembly 10 includes a generally cup-shaped housing whichincludes an axial hub 21 and a tubular mounting cylinder 22 telescopedon the hub and attached by a mounting nut 23 and four flathead screws 24(only two shown). The mounting cylinder 22 acts as a base for theoperative components of the stationary assembly. Two terminals 25, 25are provided in the rear of the housing for electrical connections to adc. power supply.

The armature winding means 26 is carried on the mounting cylinder 22 andfastened to the same by a washer 27 and a threaded nut 28. The armature26 includes a plurality of coils or windings distributed about the motoraxis to produce a rotating magnetic field when selectively connected tothe external dc. power supply. In this instance, 33 commutator bars 29(only two shown) are attached to the armature 26 in anequiangularly-spaced, circular arrangement. Each commutator bar 29 iselectrically connected to the one end of each of two winding groups. Thewindings are selectively connected to the external power supply throughstationary switches in electrical contact with the commutator bars, theconstruction and operation of these switches will subsequently bedescribed in detail.

The rotating assembly 40 is connected to the stationary assembly 10while being freely revolvable through the action of two ball bearings30, 31.

The outer races of the two ball bearings 30, 31 sit in bearing seats 32,33 in the inner diameter of the mounting cylinder 22. The front bearing30 sits against a shoulder 34 in the flanged shaft 50 which is the basefor the rotating assembly 40. The

front bearing 30 is trapped because its inner race sits against theshoulder 34 in the flanged shaft 50 and its outer race sits against ashoulder 35 in the mounting cylinder 22. A tube 37 separates andpreloads the two bearings by seating against the other side of the innerrace of the front bearing 30 and the inner race of the back bearing 31.The end play of the flanged shaft is determined by the dimensionaldifference between the length of the tube 37 and the distance betweenthe bearing shoulders 35, 36 inside the mounting cylinder 22. Thebearings 30, 31 and the flanged shaft 50 are trapped by a washer 38 anda nut 39 on the end of the flanged shaft 50 driven against the innerrace of the back bearing 31.

The rotating assembly 40 includes a permanent magnet motor field 51attached to the flanged shaft 50 in such a position that it encirclesthe armature field 26. The motor field 51 is attached to the flangedshaft 50 by four flathead screws 52 (only two shown).

In accordance with the present invention, a magnet and plate assembly 60operates in conjunction with two arrays of magnetic reed switches 80,81. These switches carry the current from the external source to thearmature so that a rotating magnetic field is produced in the armature26. The operation of the motor is caused by the interaction of thearmature field with the permanent magnet field 51.

As shown in greater detail in FIG. 2, the front printed circuit board iscircular in shape and has a continuous copper strip 72 near its outeredge and 33 equally-spaced copper segments 74 located near the center ofthe board 70. Thirty-three reed switches 80 are mounted to the board ina circular array, wherein the switches are equi-angularly spaced andradially elongated. One end of each reed switch is connected to thecontinuous copper strip 72 which serves as a common terminal and theother end is connected to a corresponding one of the inner coppersegments 74. The continuous copper strip 72 is electrically connected tothe negative terminal of the motor.

The circular rear printed circuit board 71 is spaced apart from but onthe same axis as the front printed circuit board 70. The rear board 71has a continuous copper strip 73 near its outer edge and 33equally-spaced copper segments 75 located near the center of the board71. Thirtythree reed switches 81 are mounted to the board 71 in acircular array, wherein the switches are equiangularly spaced andradially elongated. One end of each reed switch is connected to thecontinuous copper strip 73 which serves as a common terminal and theother end is connected to a corresponding one of the inner coppersegments 75. The continuous copper strip 73 is electrically connected tothe positive terminal 25 of the motor.

Each copper segment 74 on the front board 70 has a male contact 76pressed through it and a conductive contact spring 77 soldered to itsback. The 33 contact springs 77 line up with the 33 commutator bars 29on the rotor. Each spring makes electrical contact with one commutatorbar.

Each copper segment on the rear board has a female electrical socket 78pressed through it. The male contacts 76 in the front board 70 mate withthe female sockets 78 in the rear board 71. Therefore, when the front orrear switch of two commonly-connected switches is closed, current willpass into the contact spring 77 and through to the commutator segment29. Each commutator segment 29 contains two armature winding groups. Anarmature winding group is energized when the switches connected to bothof its terminals are closed.

The actuating magnet and plate assembly 60 is attached to the flangedshaft 50 by eight .flathead screws 65 (only two shown) and rotates withit. As shown in detail in FIG. 3, two in this instance, individualpermanent magnets 62, 63, comprising a single actuator are cemented intoeach of two recessed areas on each side of the mounting plate;therefore, there are two actuator magnet locations on each side of theplate. At each actuator magnet location, a mumetal lamination assembly64 is cemented into a recessed area behind each of the magnets on theopposite side of the mounting plate 60; these mumetal laminations 64serve as magnetic shields so that the magnetic action on the switchesoperates solely in one direction. The axial location of the magnet andplate assembly 60 and the two assembled printed circuit boards 70, 71 issuch that there is in this instance a 0.015 inch to 0.020 inch air gapbetween the magnets in the mounting plate and the reed switches on thetwo printed circuit boards.

The above construction results in a pair of actuating magnet locationsfacing the reed switches on the front printed circuit board 70, and theother pair of magnet locations on the other side of the magnet and plateassembly facing the reed switches on the rear printed circuit board 71.The radial position of each magnet location is such that the center ofthe magnets pass by the center of the reed switches, so that themagnetic field operates the switches. The two magnet locations facingthe front board 70 are separated in this instance by 90, as are thelocations facing the rear board 71. In this embodiment, the relativeangular positions of the magnet locations are 90, 135 and 225.

The operation of the motor shown in FIG. 1 is as follows: Current flowsfrom the positive side of the dc. power supply to the positive terminal25 of the motor and then to the continuous copper strip 73 on the rearprinted circuit board 71. The dc. current then flows through the reedswitches 81 which have been closed on the rear printed circuit board bythe actuating magnets in the magnet and plate assembly facing the rearprinted circuit board. The current then passes through the femaleelectrical sockets 78 at the base of the closed reed switches and to themating male contacts 76 in the front printed circuit board 70, thenthrough the contact springs 77 attached to those particular maleelectrical contacts. The current then flows from the contact springs 77through the contacted commutator bars 29. From the commutator bars thecurrent flows into and energizes the windings which have both endsplaced into circuit by the closure of the proper switches, one in thefront board 70, and one in the rear board 71. Current flows throughthese windings out to the respective commutator bar. The current thenflows from these commutator bars 29 to the springs 77 in contact withthem and continues through the reed switches 80 on the front printedcircuit board 70 which have been closed by the magnets facing the frontprinted circuit board. The current flows out of the closed reed switcheson the front circuit board to the continuous conductive strip 72 on theboard and out through the leadwire connected to this strip to thenegative terminal 25 on the housing and then out to the negative side ofthe dc. power supply.

Current flow in the coils of the armature produces a magnetic fieldwhich interacts with the magnetic field set up by the permanent magnetmotor field. This interaction produces rotation of the flanged shaft.Rotation is continuous because the magnets in the magnet and plateassembly are located in such a manner that the initially-closed reedswitch does not open before the adjacent reed switch in the line ofrotation is closed. If the connections from the dc. power supply to theterminals on the motor housing are reversed, the direction of rotationof the motor will reverse.

It is to be understood that a motor can be constructed according to thisinvention whereby the flanged shaft with its attaching parts isstationary, while the mounting cylinder with its attaching parts isrotating. The necessary power is supplied to the rotating printedcircuit boards by contacts sliding on slip rings.

In the arrangement of FIG. 4, the windings of the rotor are connecteddirectly to the reed switches 101. The contact is made through thecopper segment array 102. This construction eliminates the need forcommutator bars or contact springs.

The apparatus constructed according to this invention could beoperatedas a dc. generator. If the rotating member is driven by an externaldrive member, then the apparatus will generate a dc. voltage.

Thus, while preferred constructional features of the invention areembodied in the structure illustrated herein, it is to be understoodthat changes and variations may be made by those skilled in the artwithout departing from the spirit and scope of the appended claims.

What is claimed is:

1. In a direct current motor that includes permanent magnet motor fieldmeans rotatable about a central axis and a stationary armature windingmeans for producing rotary movement about said common central axis inresponse to a changing polarity current in said armature winding means,said armature winding means having a plurality of winding groupsdistributed about said axis; a first circular array of angularlyaligned,normally-open, magnetic reed switches spaced about said axis and fixedrelative to said armature winding means, said first array connected to afirst terminal and each of said switches in said first arrayindividually connected to one end of each of said winding groups througha corresponding spring in contact with a corresponding commutator barattached to the armature winding means; a second circular array ofangularly-aligned, normally-open, magnetic reed switches spaced aboutsaid axis so that each switch in said second array is opposite and apartfrom a corresponding switch in said first array and fixed relative tosaid armature winding means, said second array, connected to a secondterminal and each of said switches in said second array individuallyconnected to the other end of each of said winding groups through aspring shared with a switch in said first array connected to asubsequent winding group and the corresponding commutator bar, each ofsaid commutator bars is in electrical contact with the ends of twoarmature winding groups; and a permanent magnet actuating meanscomprising a plate rotatable in unison with said permanent magnet motorfield and carrying spaced magnets for simultaneously closing the reedswitches connected to opposite ends of a selected winding group andsequentially actuating each of said winding groups said first arrayconsisting of 33 reed switches and said second array consisting of 33reed switches.

2. Apparatus as in claim 1 wherein the said plate of the per manentmagnet actuating means contains two magnet locations on a first side ofthe plate with shielding means on the second side of the plate in backof each of the magnet locations and two magnet locations on a secondside of the plate at different angular positions from the magnets on thefirst side with shielding means on the first side in back of each ofthese second magnet locations.

3. In a direct current motor that includes permanent magnet motor fieldmeans and armature winding means for producing relative rotary movementabout a common central axis in response to a current in said armaturewinding means, said armature winding means having a number of windinggroups distributed about said axis; a first circular array comprising acorresponding number of equi-angularly spaced, radially extending,normally-open magnetic switches spaced about said axis, separate meansconnecting such of said switches of said first array to one end of acorresponding one of said winding groups; a common first terminalconnected to each of said switches, a second circular array comprising acorresponding number of equi-angularly spaced, radially extending,normally-open magnetic reed switches spaced about said axis, separatemeans connecting each of said switches of said second array to theopposite end of a corresponding one of said winding groups; a commonsecond terminal connected to each of said switches of said second array;and rotatable means mounting a plurality of first magnetic actuatingmeans for controlling operation of the switches of said first array anda plurality of second magnetic actuating means for cooperativelycontrolling operation of the switches of said second array forsimultaneously closing the ones of said switches connected to oppositeends of the same winding group, said plurality of first actuating meansbeing spaced in a predetermined angular relation about said axis todefine an open angular region of sufficient extent to span several ofsaid switches of said first array and said plurality of second actuatingmeans being spaced in a corresponding predetermined angular relationabout said axis to define an open angular region of sufficient extent tospan several of said switches of said second array, each of said firstand second actuating means being of sufficient angular span to maintainactuation of a closed switch until after the next succeeding switch ofits corresponding array is closed to provide a continuously acting forcefield of narrower spread and in more direct angular alignment with thepermanent magnet motor field means so as to impart higher continuoustorque.

4. Apparatus as in claim 3 wherein said rotatable means is a platepositioned between said first and second arrays and movable relative tosaid arrays, said plate contains first permanent magnet means facing thefirst array and constituting said first actuating means and secondpermanent magnet means facing the second array and constituting saidsecond actuating means.

5. Apparatus as in claim 4 wherein said first magnet means consists oftwo permanent magnet locations and said second magnet means consists oftwo permanent magnet locations at different but corresponding angularpositions from the locations of the first magnet means.

6. Apparatus as in claim 5 wherein a magnetic field shielding means islocated on the opposite side of the plate in back of each magnetlocation.

UNITED STATES PATENT OFFICE CERTIFICATE v OF CORRECTION Patent N9- 3,662, 196 Dated Mav 9L 1972 Inventor(s) Fred Ruschmann It is certifiedthat error appears in the above-identified patent and that said LettersPatent re hereby corrected as shown below:

Col. 4, line 74: The word "such" should be -e61c:h

Signed and sealed this 25th day of July 1972.

(SEAL) Attest: I

EDWARD M.FLET0HER, JR. ROBERT GoTTscHALK Attesting Officer Commissionerof Patents FOHM PO-1050 (IO-69) SCOMM-DC 6037B-I'L9 u s cnvummtulPumlmuolml punum 1 UNITED STATES PATENT OFFICE CERTIFICATE 0F CORRECTIONPatent No. 3 662 196 Dated Mav 9 L 1972 InVent0I(S) Fred Ruschmann It iscertified that error appears in the above-identified patent and thatsaid Letters Patent are hereby corrected as shown below:

Col. 4, line 74: The word "such" should be each Signed and sealed this25th day of July 1972.

(SEAL) Attest:

EDWARD M.FLETC HER, JR.

ROBERT GOTTSCHALK Attesting Officer Commissioner of Patents 'ORM PO-IOSO(10-6

1. In a direct current motor that includes permanent magnet motor fieldmeans rotatable about a central axis and a stationary armature windingmeans for producing rotary movement about said common central axis inresponse to a changing polarity current in said armature winding means,said armature winding means having a plurality of winding groupsdistributed about said axis; a first circular array ofangularly-aligned, normally-open, magnetic reed switches spaced aboutsaid axis and fixed relative to said armature winding means, said firstarray connected to a first terminal and each of said switches in saidfirst array individually connected to one end of each of said windinggroups through a corresponding spring in contact with a correspondingcommutator bar attached to the armature winding means; a second circulararray of angularly-aligned, normally-open, magnetic reed switches spacedabout said axis so that each switch in said second array is opposite andaparT from a corresponding switch in said first array and fixed relativeto said armature winding means, said second array, connected to a secondterminal and each of said switches in said second array individuallyconnected to the other end of each of said winding groups through aspring shared with a switch in said first array connected to asubsequent winding group and the corresponding commutator bar, each ofsaid commutator bars is in electrical contact with the ends of twoarmature winding groups; and a permanent magnet actuating meanscomprising a plate rotatable in unison with said permanent magnet motorfield and carrying spaced magnets for simultaneously closing the reedswitches connected to opposite ends of a selected winding group andsequentially actuating each of said winding groups said first arrayconsisting of 33 reed switches and said second array consisting of 33reed switches.
 2. Apparatus as in claim 1 wherein the said plate of thepermanent magnet actuating means contains two magnet locations on afirst side of the plate with shielding means on the second side of theplate in back of each of the magnet locations and two magnet locationson a second side of the plate at different angular positions from themagnets on the first side with shielding means on the first side in backof each of these second magnet locations.
 3. In a direct current motorthat includes permanent magnet motor field means and armature windingmeans for producing relative rotary movement about a common central axisin response to a current in said armature winding means, said armaturewinding means having a number of winding groups distributed about saidaxis; a first circular array comprising a corresponding number ofequi-angularly spaced, radially extending, normally-open magneticswitches spaced about said axis, separate means connecting such of saidswitches of said first array to one end of a corresponding one of saidwinding groups; a common first terminal connected to each of saidswitches, a second circular array comprising a corresponding number ofequi-angularly spaced, radially extending, normally-open magnetic reedswitches spaced about said axis, separate means connecting each of saidswitches of said second array to the opposite end of a corresponding oneof said winding groups; a common second terminal connected to each ofsaid switches of said second array; and rotatable means mounting aplurality of first magnetic actuating means for controlling operation ofthe switches of said first array and a plurality of second magneticactuating means for cooperatively controlling operation of the switchesof said second array for simultaneously closing the ones of saidswitches connected to opposite ends of the same winding group, saidplurality of first actuating means being spaced in a predeterminedangular relation about said axis to define an open angular region ofsufficient extent to span several of said switches of said first arrayand said plurality of second actuating means being spaced in acorresponding predetermined angular relation about said axis to definean open angular region of sufficient extent to span several of saidswitches of said second array, each of said first and second actuatingmeans being of sufficient angular span to maintain actuation of a closedswitch until after the next succeeding switch of its corresponding arrayis closed to provide a continuously acting force field of narrowerspread and in more direct angular alignment with the permanent magnetmotor field means so as to impart higher continuous torque.
 4. Apparatusas in claim 3 wherein said rotatable means is a plate positioned betweensaid first and second arrays and movable relative to said arrays, saidplate contains first permanent magnet means facing the first array andconstituting said first actuating means and second permanent magnetmeans facing the second array and constituting said second actuatingmeans.
 5. Apparatus as in claim 4 wherein said first magnet meansconsists of two permanent magnet locations and said second magnet meansconsists of two permanent magnet locations at different butcorresponding angular positions from the locations of the first magnetmeans.
 6. Apparatus as in claim 5 wherein a magnetic field shieldingmeans is located on the opposite side of the plate in back of eachmagnet location.